1. Field of the Invention
This invention relates to water treatment systems and, in particular, to systems and methods for dewatering and thickening operations within water treatment systems.
2. Description of Related Art
One of the earliest attempts to measure floc strength was described by Hannah et al. in Measurement of floc strength by particle counting, J. AWWA. January 1967, 843-858, wherein the change in particle size distribution during the application of a known amount of shear can be used to estimate floc strength. In Higgins and Novak, The effect of cations on the settling and dewatering of activated sludges: Laboratory results, Water Environ. Res., 69 (2) (1997), 215-224 and Higgins and Novak, in Dewatering and settling of activated sludges: The case for using cation analysis, Water Environ. Res., 69 (2) (1967) 225-232, used the deterioration in the dewaterability as measured by CST (capillary suction time) test results to characterize the ability of flocs to resist shear forces. Other researchers, such as Tambo and Hozumi in Physical characteristics of flocs-II. strength of floc, Water Res., 13 (1979) 421-427, used the floc size and density to provide an indication of floc strength.
Glasgow and Hsu in An experimental study of floc strength, AICHE Journal, 28 (5) (1982) 779-785, developed a model and an apparatus for directly measuring individual floc strength from the aggregation of colloidal kaolin and either ferric chloride (FeCl3) or polymer. Yeung and Pelton in Micromechanics: A new approach to studying the strength and breakup of flocs. J. Colloid and Interface Science, 184 (1996) 579-585, developed micromechanical techniques that pull apart single floc particles (6-40 um) and determine floc strengths. Although these techniques are of great scientific value, they are typically not applicable to sludge.
Techniques for adding a treatment agent to a sludge stream using rheology have previously been disclosed, for example U.S. Pat. No. 5,003,814 by Crawford et al. Also, Dentel in Evaluation and role of rheological properties in sludge management, Water Sci. Technol., 36 (11) (1997) 1-8, offers an review of rheology and its use in sludge treatment and processing applications.
The work of Lee and co-workers (2002) deserves attention. Yen et al. in Network strength and dewaterability of flocculated sludge, Water Res., 36 (2002) 539-550, tried to correlate the area of the hysteresis loop principle from the rheological data, which is obtained by first increasing and then decreasing the rotational speed of the rheometer spindle, to the network strength of sludge. The researchers realized that the area of the hysteresis loop could not represent the network strength. They calculated the total and specific energy input to the suspension, where the specific energy input was defined as the energy required to break down the sludge network. The hysteresis loop was used to determine the specific energy. Yen et al. correlated the network strength to the polymer dose, where increasing the polymer dose resulted in an increase in the network strength. Yen et al. used a concentric cylinder rheometer and offered no data concerning the reproducibility of the produced rheogram while Abu-Orf and Dentel, in Rheology as a Tool for Polymer Dose Assessment and Control, J. Envir Engrg, ASCE, 125, No. 12 (1999), 1133-1141, has documented that reproducibility with these measurements is a concern.